Memory mapping for parallel turbo decoding

ABSTRACT

A routing multiplexer system provides p outputs based on a selected permutation of p inputs. Each of a plurality of modules has two inputs, two outputs and a control input and is arranged to supply signals at the two inputs to the two outputs in a direct or transposed order based on a value of a bit at the control input. A first p/2 group of the modules are coupled to the n inputs and a second p/2 group of the modules provide the n outputs. A plurality of control bit tables each contains a plurality of bits in an arrangement based on a respective permutation. The memory is responsive to a selected permutation to supply bits to the respective modules based on respective bit values of a respective control bit table, thereby establishing a selected and programmable permutation of the inputs to the outputs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority from applicationSer. No. 10/648,038, filed Aug. 26, 2003, for “Memory Mapping ForParallel Turbo Decoding” by Alexander E. Andreev, Anatoli A. Bolotov andRanko Scepanovic and assigned to the same assignee as the presentapplication, the disclosure of which is herein incorporated byreference.

Cross reference is also made to application Ser. No. 10/299,270, filedNov. 19, 2002 and issued as U.S. Pat. No. 7,096,413, for “Decomposer forParallel Turbo Decoding, Process and Integrated Circuit” by Alexander E.Andreev, Ranko Scepanovic and Vojislav Vukovic and assigned to the sameassignee as the present application, the disclosure of which is hereinincorporated by reference.

FIELD OF THE INVENTION

This invention relates to circuits that map memories for parallel turbodecoding.

BACKGROUND OF THE INVENTION

Turbo code systems employ convolutional codes, which are generated byinterleaving data. There are two types of turbo code systems: ones thatuse parallel concatenated convolutional codes, and ones that useserially concatenated convolutional codes. Data processing systems thatemploy parallel concatenated convolutional codes decode the codes inseveral stages. In a first stage, the original data (e.g. sequence ofsymbols) are processed, and in a second stage the data obtained bypermuting the original sequence of symbols is processed, usually usingthe same process as in the first stage. The data are processed inparallel, requiring that the data be stored in several memories andaccessed in parallel for the respective stage.

However, parallel processing often causes conflicts. If two or moreelements or sets of data that are required to be accessed in a givencycle are in the same memory, they are not accessible in parallel.Consequently, the problem becomes one of organizing access to the dataso that all required data are in different memories and can besimultaneously accessed in each of the processing stages.

Consider a one dimensional array of data, DATA[i]=d_i, where i=0, 1, . .. , NUM−1. Index i is also called a global address. If two interleavertables, I_0 and I_1, have the same size with N rows and p columns, allindices or global addresses 0, 1, . . . , NUM−1 can be written to eachof these tables in some order determined by two permutations. A processof data updating is controlled by a processor, whose commands have theform COM=(TABLE, ROW, OPERATION), where TABLE is I_0 or I_1, ROW is arow number, and OPERATION is a read or write operation.

FIG. 1 illustrates an example of interleaver tables I_0 and I_1. Acommand COM (I_0,0,READ) means that row r_0=(25,4,27,41,20) is takenfrom table I_0, and then data DATA[25], DATA[4], DATA[27], DATA[41],DATA[20] are read from the array DATA. In the case of commandCOM=(I_1,3,WRITE), the processor takes global addresses from rowr_3=(12,37,9,32,36) in table I_1, and writes some updated data d_new_0,d_new_1, d_new_2, d_new_3, d_new_4, into array DATA at these globaladdresses, that is, the processor updates (writes) data in the array,DATA[12]=d_new_0, DATA[37]=d_new_1, DATA[9]=d_new_2, DATA[32]=d_new_3,DATA[36]=d_new_4.

During the process of turbo decoding the processor performs a sequenceof commands over data in the array DATA. The aforementioned Andreev etal. application describes a decomposer for parallel decoding using nsingle port memories MEM_0, . . . , MEM_(n−1), where n is the smallestpower of 2 that is greater than or equal to N and N is the number ofrows in tables I_0 and I_1. The Andreev et al. technique creates a tableF that represents each memory in a column, such as MEM_0, . . . , MEM_7shown in FIG. 1, and a global address at each memory address addr in thememory. Two tables G_0 and G_1, which are the same size as tables I_0and I_1 contain entries in the form (addr, mem) that points to memoryMEM_mem and to the address addr related to the memories depicted intable F.

Consider the processor command COM=(I_0, 0, R). Row number 0, R_0=(0,5),(0,0), (0,3), (0,7), (0,4), is taken from table G_0 and the processorsimultaneously reads

As shown in table F, MEM_5 (sixth column of table F), address 0 (firstrow), contains the global index 25, MEM_0, addr_0 contains index 4, etc.Table F thus provides a correspondence between global addresses (arrayindices) and local addresses (memory addresses). Thus, {*} means thatthe read operation is simultaneously performed with global addresses25,4,27,41,20, as it should be. {*} also shows that after reading thememories, the global addresses must be matched to the local addresses.

FIG. 2 illustrates a multiplexer 10 that transposes the global addressesor indices from a natural order to a permuted order. Thus, in FIG. 2 theindex for the 0 data element (value) of the permutation is read fromMEM_5, the index for the 1 value is read from MEM_0, etc. Thus, aselection of required values is output from the memories and apermutation of those values is performed by multiplexer 10.

SUMMARY OF THE INVENTION

The present invention is directed to a global routing multiplexer thatis capable of selecting p values among n given values and then make apermutation of them according to a given permutation of the length p,while both operations are performed dynamically, i.e. during execution.The global routing multiplexer according to the present invention isimplemented in an integrated circuit in minimal chip area and withoutdegrading timing characteristics.

In one embodiment of the invention, a routing multiplexer systemprovides p outputs based on a selected permutation of p inputs. Eachmodule of an array of modules has two inputs, two outputs and a controlinput. Each module is arranged to supply the inputs to the outputs in adirect or transposed order based on the control input. A first p/2 groupof the modules is coupled to the p inputs and a last p/2 group of themodules is coupled to the p outputs. A memory contains a plurality ofcontrol bit tables each containing bit values in an arrangement based ona respective permutation. The memory is responsive to the selectedpermutation to supply bits from a respective control bit table to therespective modules.

In some embodiments, the multiplexer system is embodied in an integratedcircuit chip and is used to map p input memories for parallel turbodecoding. Map inputs couple an output of each memory to respective onesof the inputs of the first group of the modules, and map outputs arecoupled to respective ones of the outputs of the last group of themodules.

In another embodiment of the invention, a control bit table for therouting multiplexer is formed by defining the selected permutationhaving length n, where n≧p. First and second groups of vertices areidentified, each containing alternate vertices of a graph of theselected permutation. First and second permutations are calculated basedon the respective first and second groups of vertices. The control bittable is formed based on the first and second permutations and on thevertices of the graph of the selected permutation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are illustrations useful in explaining certain principlesof memory mapping for parallel turbo decoding.

FIGS. 3 and 4 are illustrations useful in explaining certain principlesof a global routing multiplexer according to the present invention.

FIGS. 5-12 are illustrations useful in explaining development of controlbit tables used in a global routing multiplexer according to the presentinvention.

FIG. 13 is a flowchart of a process of construction of a control bittable for a global routing multiplexer according to an embodiment of thepresent invention.

FIG. 14 is a block diagram of a module used in construction of a globalrouting multiplexer according to the present invention.

FIG. 15 is a block diagram of a global routing multiplexer according toan embodiment of the present invention.

FIG. 16 is a block diagram of the multiplexer shown in FIG. 15 coupledto a memory containing control bit tables constructed by the process ofFIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A control bit table T is constructed for each row of tables G_0 and G_1(FIG. 1). The control bits are applied to control inputs of a globalrouting multiplexer to create a multiplexer in the form of that depictedin FIG. 2. The computation of control bit tables for all rows from bothtables G_0 and G_1 (as far as the computation of the tables F, G_0 andG_1 themselves) can be done in advance and the tables can be stored inan auxiliary memory. The control bit table T (written as a vector)computed for the row R_i of the table G_0 is stored in the auxiliarymemory at an address (0,i), and for the row R_i from the table G_1 at anaddress (1,i) respectively, where i=0, 1, 2, . . . , N−1.

For the purposes of explanation, n is the number of single-port memoriessupplying a single element or value and p is the length, or number ofvalues, of the permutation. Consider first a global routing multiplexerfor n>p, herein designated GR_MUX(n.p). Multiplexer GR_MUX(n.p) istransformed into multiplexer GR_MUX(n.n) that realizes a permutation oflength n. This can be done by adding n-p fictive outputs to the rightside of the GR_MUX(n.p) to change the initial permutation of length p tothe larger permutation of the length n. For example, a multiplexerGR_MUX(8.5) (FIG. 2) is converted to a multiplexer GR_MUX(8.8) by addingthree fictive outputs and coupling them to the unnecessary inputmemories MEM_3, MEM_4 and MEM_5. See FIG. 3. After completion ofsynthesis these extra outputs (and unneeded cells connected with themand associated control bits) can be removed from the chip.

FIG. 4 illustrates a global routing multiplexer 20 that has thecapability to realize any permutation of a given length of inputs,namely to interconnect the inputs with outputs in some specified,permuted order. Multiplexer 20 has control inputs 22 for control bits aswell as n inputs 24 and n outputs 26 to be interconnected in an orderspecified by the control bits at inputs 22. As shown in FIG. 4, inputs0, 1, . . . , n−1 are transformed to outputs 0, 1, . . . , n−1 in apermuted order, which in the example of FIG. 4 shows input 0 connectedto output 1, input n−1 connected to output 2, etc.

The control bits permit reconfiguration, or adjustment, of the internalstructure of the multiplexer 20. More precisely, for any permutation Pof inputs 24 there exists a set of control bits that can be applied tocontrol inputs 22 to configure multiplexer 20 to perform permutation Pand provide outputs 26 based on that permutation. In one sense, themultiplexer appears as a programmable multiplexer that is programmableby the set of control bits; in another sense, the multiplexer appears asa universal multiplexer to realize any permutation of a given length.

The control bits that form the multiplexer's “program” may bepre-computed and written into an external memory module. The controlbits are read from that memory and programmatically switch themultiplexer to the required configuration for the desired permutation.In one form of the invention, the control bits are arranged in controlbit tables for each permutation, which are stored in the memory. Theflexibility of the programmable multiplexer makes it especially usefulin such applications that make use of field programmable gate arrays(FPGAs), programmable logic modules (PLM), etc.

For an understanding of global routing multiplexer 20, it is firstnecessary to understand the coding of permutations, and particularly theapplication of coloring and decomposing techniques used in the recursiveconstruction of the control bit tables.

1. Coloring of Permutations

Consider permutations of n numbers from the set {0, 1, . . . , n−1}.Permutation P, comprising P(0)=i_0, P(1)=i_1, . . . , P(n−1)=i_(n−1), isdenoted by an ordered n-tuple (i_0, i_1, . . . , i_(n−1), where i_0,i_1, . . . , i_(n−1) are numbers 0, 1, . . . , n−1 written in someorder. Number n is the permutation length. For example,P=(7,1,0,6,2,5,3,4) is a permutation of the natural order(0,1,2,3,4,5,6,7) having a length n=8.

To color permutation P=(i_0, i_1, . . . , i_(2m−1)) of even length 2m,consider a graph G with 2m vertices corresponding to numbers 0, 1, . . ., 2m−1. Alternate m edges (0,1), (2,3), . . . of this graph are formedby connecting vertices 0 and 1, . . . , 2 and 3, etc. These edges arereferred to as black edges, and their construction does not depend onthe permutation itself. Again using permutation P, yet another alternatem edges (1,2), (3,4), . . . are formed by connecting vertices 1 and 2, .. . , 3 and 4, etc., and are referred to as red edges. As far as P is apermutation, each vertex i is incident to exactly 1 black and 1 rededge. This implies that graph G is a union of several cycles each ofeven length (see FIG. 5 where red edges are depicted in dashed lines andblack edges are depicted in solid lines).

By moving along these cycles in some direction, each passing vertex i iscolored in the outgoing edge's color (see FIG. 6, where black verticesare denoted by 0 and red ones are denoted by 1). The color of a vertex iis designated as Color(i).

FIG. 7 illustrates a graph G for permutation P=(7,1,0,6,2,5,3,4) withred and black edges. Thus the black edges are (0,1), (2,3), (4,5) and(6,7) and the red edges are (1,2), (3,4), (5,6) and (7,0), and are notdependent on permutation P. As illustrated in FIG. 8, the graph of FIG.7 reduces to two cycles which leads, for instance, to the coloring ofgraph's vertices shown in FIG. 9, where colors 0 (black) and 1 (red) aredepicted in brackets adjacent the vertices.

2. Decomposing of Permutations

Two new permutations P_0 and P_1, each of length m, can be extractedfrom a correctly colored graph G of permutation P of length 2m. Fromsome starting point in the graph G, the m black numbers are recorded ina row L_0 and assigned j_0, . . . , j_(m−1), in the order of passing ofthe respective black vertices. Similarly, the m red numbers are recordedin a row L_1 and assigned k_0, . . . , k_(m−1), in the order of passingof the respective red vertices. Thus, row L_0=(j_0, . . . , j_(m−1)) androw L_=(k_, . . . , k(m_1)), and each is in the order of thepermutation. Stated another way, one of the two numbers defining anedge, (0,1), (2,3), . . . , (2m−2, 2m−1), is black and goes to row L_0,and the other number is red and goes to row L_1.

The numbers of both rows L_0 and L_1 are divided (as integers) by 2, andthe result is rounded down to j and k, respectively: dividing 2j and2j+1 by 2 results in j and dividing 2k and 2k+1 by 2 results in k. As aresult, two permutations P_0=(j_0/2, . . . , j_(m−1)/2) and P_1=(k_0/2,. . . , k_(m−1)/2) are derived by dividing the numbers in rows L_0 andL_2 by 2 and rounding down.

This is exemplified in FIG. 7, where permutationP=(7(0),1(1),0(0),6(1),2(0),5(1),3(1),4(0)) provides rows L_=(7,0,2,4)and L_1=(1,6,5,3). Two permutations P_0=(3,0,1,2) and P_1=(0,3,2,1) ofnumbers {0,1,2,3} are derived by dividing the numbers of each row by 2(rounded down).

3. Construction of Control Bit Tables T(P)

Though control bit tables may be built for permutations of arbitrarylength n, what follows is a description of a control bit table forpermutations where length n is a power of 2.

Control bit table T(P) for a given permutation P of a length n has asize (2k−1)×2^(k-1) and consists of 2k−1 rows each having length equalto 2^(k-1), where n=2^(k) and k>0. This table consists of ones andzeroes and is built recursively for a given permutation P. Considercontrol bit tables T constructed for permutation P having a length n=8.In this case, k=3, and table T will have a size of 5×4 (5 rows eachhaving a length of 4 bits).

For k=1 there are two permutations only, namely (0,1) and (1,0). For thefirst permutation T=(0) and for the second T=(1).

For k>1, the permutation P of length n=2^(k) can be colored as describedabove, and decomposed into two permutations P_0 and P_1, each having alength 2^(k-1). Control bit tables T_0 and T_1 are then constructed forpermutations P_0 and P_1, respectively. Control bit tables T_0 and T_1may be constructed using global permutation networks described at pp.309-311 in MODELS OF COMPUTATION—Exploring the Power of Computing, byJohn E. Savage, Addison-Wesley (1998), incorporated herein by reference.One of the two colors, black for instance, is chosen as the leadingcolor, designated label_color. Thus, if black is the leading color,label_color=0.

A differently colored pair of numbers (i,j) is “well ordered” ifColor(i)=label_color. Otherwise, the pair is “disordered”. The wellordered pairs are labeled with a label index of 0 and disordered pairsare labeled with a label index of 1.

For a given order of elements, pairs (i_0, i_1), . . . , (i_(n−2),i_(n−1)) are labeled to determine label indices in a row S of length2^(k-1). The first term of each pair identifies whether the pair is wellordered or disordered, thereby defining the bits of the row S. A firstrow, S_0, is created based on the order of input memories to themultiplexer (which is usually the natural order of the input memories).S_0=(a_0, . . . , a_(m−1)), where m=2^(k-1) and a_i is a label index ofthe pair (2i, 2i+1). In the example, the order of memory inputs to themultiplexer is the natural order and is 0,1,2,3,4,5,6,7. See FIG. 3.Consequently, S_0 is derived from the pairs (0,1),(2,3),(4,5),(6,7).

For a given permutation P=(i_0, . . . , i_(n−1)) pairs (i_0,i_1), . . ., (i_(n−2),i_(n−1)) determine the row of label indices S_1=(b_0, . . . ,b_(m−1)). Thus permutation P=(7,1,0,6,2,5,3,4) provides the pairs(7,1),(0,6),(2,5),(3,4). The first term of each pair indicates whichamong the pairs is well ordered or disordered, thereby defining the bitsof rows S_0 and S_1.

With reference to FIGS. 10-12, for the above colored and decomposedpermutation P=(7,1,0,6,2,5,3,4) only last pair (6,7) of the naturalpairs (0,1), (2,3), (4,5), (6,7) is disordered, so line S_0 of labelindices will be S_0=(0,0,0,1). More particularly, with reference to FIG.9, each of the pairs (0,1), (2,3) and (4,5) has its first number coloredblack (0). Therefore, these pairs are well ordered (value=0). Howeverthe pair (6,7) has its first number (6) colored red (1), meaning it isdisordered (value=1). In a similar manner, pairs (7,1), (0,6), (2,5) and(3,4) of permutation P provide S_1=(0,0,0,1).

This leads to table T (FIG. 11) where T_0 and T_1 are 3×2 control bittables for permutation P_0 and P_1. Tables T_0 and T_1 are concatenated,and rows S_0 and S_1 are inserted as the first and last rows of thetable, resulting in the control bit table T for the permutation P, asshown in FIG. 12.

The process of building control bit tables for permutations can beconsidered as a coding permutations of length n=2^(k) by binary tablesof size (2k−1)×2^(k-1), where k>0. As shown in FIG. 13, the processcommences at step 100 with the selection of a permutation P of length n,where n is an even number equal to 2m.

Permutation P is colored at step 110. More particularly, at step 112 agraph for permutation P is constructed having 2m vertices and edges. Theorder of the vertices is the order of the permutation, as shown in FIG.7. At step 114, alternate vertices are assigned different status, suchas colors black and red. As previously explained, one technique toaccomplish this is to color alternate edges black and red and assigneach vertex the same color as its outgoing edge.

At step 120, permutation P is decomposed. More particularly, at step 122the red vertices are assigned to row L_0 and the black vertices areassigned to row L_1, both in the same order as they appear in thepermutation. At step 224, permutations P_0 and P_1 are calculated bydividing each value appearing in rows L_0 and L_1, respectively, by 2,rounding down. In the example given where L_0=(7,0,2,4) andL_1=(1,6,5,3), P_0=(3,0,1,2) and P_1=(0,3,2,1).

The control bit table T is constructed at step 130. More particularly,at step 132 tables T_0 and T_1 are constructed for each permutation P_0and P_1, such as in the manner described in the aforementioned Savagebook. At step 134, row S_0 is constructed based on the color of theleading vertex of vertex pairs in the natural order of vertices, and rowS_1 is constructed based on the color of the leading vertex of vertexpairs in permutation P. If the color indicates the pair is well ordered,as evidenced in the example by a leading black vertex in the pair, thebit in the row is one binary value, such as 0. If the color indicatesthe pair is disordered, as evidenced in the example by a leading redvertex in the pair, the bit is the other binary value, such as 1. Hence,in the example, S_0 is (0,0,0,1) and S_1 is (0,0,0,1).

Control table T is constructed at step 136 as a concatenation of T_0 andT_1, and rows S_0 and S_1 are inserted as the top and bottom rows oftable T. See FIG. 12. At step 140, table T is stored in memory, such asmemory 50 in FIG. 16.

The logarithm (on base 2) of the number of all permutations of thelength n, log n!, is asymptotically equal to n log n=2^(k)k which isasymptotically equal to the size of control bit table T. This means thatcoding permutations using the control bit tables turns out to be anoptimal one.

The choice of label_color is arbitrary and the choosing of another color(black instead of red or vice versa) results in a dual control bit tableconstruction. Moreover, at each step of induction the choice oflabel_color can be changed so that different control bit tables may beused for the same permutation.

4. Construction of Global Routing Multiplexer 20

FIG. 14 illustrates a basic module 30 having two inputs a and b, acontrol input c and two outputs x and y. Module 30 operates to supplyinputs a and b to outputs x and y, in either direct or transposed order,depending on the value of input c. If c=0 then module 30 does not changethe order of the inputs, and x=a and y=b. If c=1, then module S performsa transposition of the inputs, and x=b and y=a. Formally, thefunctioning of the module 30 is determined by the following system ofBoolean equations:x=(˜c)&a|c&b,y=c&a|(˜c)&b.where ˜, & and | are Boolean operations of negation, conjunction anddisjunction, respectively.

As shown in FIG. 15, global routing multiplexer 20 is constructedrecursively using (2k−1)×2^(k-1) modules 30 arranged in 2k−1 horizontalrows such that each row contains 2^(k-1) modules 30. Hence, modules 30are arranged in the same array organization as control bit table T_k.Hence, in FIG. 15, each module 30 is designated with a row and positiondesignation between 30_(1,1) and 30_((2k−1),2^(k-1)) designating rowsbetween 1 and 2k−1 and positions between 1 and 2^(k-1). For simplicity,modules 32 and 34 designate groups of modules 30 arranged in the samemanner.

FIG. 16 illustrates a memory 50 containing a plurality of control bittables T_k have a construction illustrated in FIG. 12. Memory 50 iscoupled to global routing multiplexer 20 to decode a given permutation Pselected by permutation selector 52 using the control bit table T_k forthe selected permutation P. More particularly, for a given permutationP, control bits from a corresponding control bit table T_k in memory 50are applied through bus 54 to corresponding control inputs c (FIG. 14)of corresponding modules 30 of global routing multiplexer 20. Hence, abit from row i, column j of table T_k is applied to the control input cof the module 30 located at row i, column j of multiplexer 20. Thus,numbers 0, 1, . . . , n−1 applied to the inputs of global routingmultiplexer 20 will realize some permutation based on the control bitsfrom the table T_k corresponding to the permutation.

While the present invention has been described in connection withpermutations of length n, the global routing multiplexer 20 according tothe present invention, and its attendant control bit tables, can beconstructed for shorter permutations of length p, where p<n. Moreparticularly, as described in connection with FIGS. 2 and 3, amultiplexer of length n can be designed using n-p fictive outputs (andinputs, if necessary) and the unnecessary outputs and modules 30 areremoved after synthesis. The integrated circuit forming multiplexer 30is thus reduced in size to accommodate permutations of length p. Sincecontrol bit tables are not needed for permutations affected by theexpansion of the multiplexer (i.e., permutations affecting outputsgreater than p), those tables need not be even constructed, or ifconstructed need not be placed in memory 50.

Thus the present invention provides a multiplexer system having an arrayof modules 30 arranged in 2k−1 rows, with the first row containing p/2modules coupled to the input memories being mapped and the last rowcontaining p/2 modules forming the output of the multiplexer system,where p=2^(k).

It is clear (and can be proven by induction), that if table T is builtas the control bit table for permutation P, and global routingmultiplexer 20 is built for table T, then global routing multiplexer 20realizes exactly permutation P, P→T→30→P. Multiplexer 20 has 2k−1horizontal rows of modules 30. Consequently, its depth is logarithmic,which is an optimal (by order) depth.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A process of forming a control bit table for arouting multiplexer that provides outputs based on a selectedpermutation of inputs, the process comprising steps of: a) defining theselected permutation of n values, where n is an integer variable greaterthan zero, and constructing a graph of the selected permutation, whereinthe graph comprises n vertices, corresponding to respective values ofthe selected permutation, which are connected together by n edges in anorder based on the selected permutation; b) identifying first and secondgroups of vertices each containing alternate vertices of a graph of theselected permutation; c) calculating a first permutation containing thevalues corresponding to the first group of vertices in an order definedby the selected permutation, and calculating a second permutationcontaining the values corresponding to the second group of vertices inan order defined by the selected permutation; d) forming the control bittable in a control memory, wherein the control bit table comprisescontrol bits that are based on the first and second permutations and onthe vertices of the graph of the selected permutation; and e) applyingthe control bits of the control bit table from the control memory tocontrol inputs of the routing multiplexer.
 2. The process of claim 1,wherein step b) is performed by steps of: b1) assigning a first type tofirst alternate edges along the graph and a second type to secondalternative edges so that each vertex is connected to an incoming edgehaving one type and an outgoing edge having a different type, and b2)assigning each vertex the type of one of the incoming or outgoing edges.3. The process of claim 2, wherein step c) is performed by steps of: c1)assigning the vertices having the first type to a first row andassigning the vertices having the second type to a second row, thevertices in each row being arranged in the order defined by the selectedpermutation, c2) calculating the first and second permutations based onthe values of vertices in the respective first and second rows.
 4. Theprocess of claim 3, wherein the first permutation comprises valuesrelated to one-half the values of the vertices in the first row and thesecond permutation comprises values related to one-half the values ofthe vertices in the second row.
 5. The process of claim 3, wherein stepd) is performed by steps of: d1) calculating first and second partialcontrol bit tables based on the respective first and secondpermutations, d2) pairing the vertices in a natural order, d3) pairingthe vertices in the order of the selected permutation, d4) selectingbits of a first bit string based on the type of a selected vertex ofeach pair of vertices of the natural order, d5) selecting bits of asecond bit string based on the type of a selected vertex of each pair ofvertices of the selected permutation, d6) providing the first and secondbit strings as the first and last rows, respectively, of the control bittable, and d7) concatenating the first and second partial control bittables as one or more rows of the control bit table between the firstand last rows.
 6. The process of claim 1, wherein step c) is performedby steps of: c1) assigning the vertices of the first group to a firstrow and assigning the vertices of the second group to a second row, thevertices in each row being arranged in the order defined by the selectedpermutation, c2) calculating the first and second permutations based onthe values of vertices in the respective first and second rows.
 7. Theprocess of claim 6, wherein the first permutation comprises valuesrelated to one-half the values of the vertices in the first row and thesecond permutation comprises values related to one-half the values ofthe vertices in the second row.
 8. The process of claim 1, wherein stepd) is performed by steps of: d1) calculating first and second partialcontrol bit tables based on the respective first and secondpermutations, d2) pairing the vertices in a natural order, d3) pairingthe vertices in the order of the selected permutation, d4) selectingbits of a first bit string based on a type of a selected vertex of eachpair of vertices of the natural order, d5) selecting bits of a secondbit string based on the type of a selected vertex of each pair ofvertices of the selected permutation, d6) providing the first and secondbit strings as the first and last rows, respectively, of the control bittable, and d7) concatenating the first and second partial control bittables as one or more rows of the control bit table between the firstand last rows.
 9. The process of claim 1, wherein the routingmultiplexer has p inputs and p outputs and wherein the method furthercomprises: f) forming an integrated circuit for mapping input memoriesfor parallel turbo decoding by employing a plurality of the control bittables each control bit table having at least (2k−1)×2^(k-1) bits,wherein k is an integer greater than zero and wherein formingcomprises: 1) forming a multiplexer having a plurality of modules eachmodule having first and second inputs, first and second outputs and acontrol input coupled to the control memory to receive a respective bitfrom one of the plurality of control bit tables, each module beingarranged to supply signals at the first and second inputs to the firstand second outputs in a direct or transposed order based on a value ofthe control bit at the control input, 2) coupling an output of eachinput memory to respective ones of the first and second inputs of afirst group of p/2 of the modules, and 3) selecting a respective controlbit table to supply control bits to the control inputs of the modules.10. The process of claim 9, wherein there are at least (2k−1)×2^(k-1)modules and at least (2k−1)×2^(k-1) control bits, where p=2^(k).
 11. Theprocess of claim 9, wherein the modules are arranged in an array of 2k−1rows each containing 2^(k-1) modules, and each control bit tablecontains 2k−1 rows each containing 2^(k-1) bits, where p=2^(k), whereinthe control memory supplies a j-th bit at an i-th row of a selectedcontrol bit table to the corresponding j-th module of the i-th row ofthe array.